In recent years, it has been realized that the THz region of the electromagnetic spectrum is of considerable scientific and technological interest which has lead to advances that include THz imaging (see, B. B. Hu and M. C. Nuss, “Imaging with Terahertz Waves,” Opt. Lett. 20, 1716-1718 (1995) hereby incorporated by reference), semiconductor characterization (see, D. M. Mittleman, J. Cunningham, M. C. Nuss and M. Geva, “Noncontact Semiconductor Wafer Characterization with the Terahertz Hall Effect,” Appl. Phys. Lett. 71, 16-18 (1997), hereby incorporated by reference), and chemical (see, R. H. Jacobsen, D. M. Mittleman and M. C. Nuss, Chemical Recognition of Gases and Gas Mixtures with Terahertz Waves, Opt. Lett. 21, 2011-2013 (1996), (hereby incorporated by reference) and biological sensing (see T. W. Crowe, T. Globus, D. L. Woolard and J. L. Hesler, Terahertz Sources and Detectors and Their Application to Biological Sensing, Philosophical Transactions,” Royal Society A 362, 365-377 (2004) hereby incorporated by reference. However, the THz spectrum still suffers from the often cited “THz gap,” which refers to the lack of basic components available in this frequency range. See, P. H. Siegel, THz Technology, IEEE Trans. Microwave Theory and Techniques, 50(3), 910-928, (2002), hereby incorporated by reference. This deficiency has been reduced, in part, through the use of scalable artificial electromagnetic composites such as metamaterials and frequency selective surfaces. Multifunctional electromagnetic composites derive their response primarily from the geometry of unit cells arrayed in a periodic fashion. Through ingenious design, these materials have been used to create a negative index of refraction (see, V. G. Veselago, The Electrodynamics of Substances with Simultaneously Negative Values of ∈ and μ,” Sov. Phys. Usp. 10, 509-514 (1968) and D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S. Schultz, “Composite Medium with Simultaneously Negative Permeability and Permittivity, Phys. Rev. Lett. 84, 4184-4187 (2000), both of which are incorporated by reference), perfect lens (see J. B. Pendry, Negative Refraction Makes a Perfect Lens, Phys. Rev. Lett. 85, 3966 (2000), hereby incorporated by reference), electromagnetic cloak (see D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, Metamaterial Electromagnetic Cloak at Microwave Frequencies, Science 314, 977-980 (2006), hereby incorporated by reference), perfect absorber (see N. I. Landy, et al., Perfect metamaterial absorber, Phys. Rev. Lett., 100, 207402 (2008), hereby incorporated by reference), high impedance surfaces (see D. F. Sievenpiper, L. Zhang, R. Broas, N. G. Alexopolous, E. Yablonovitch, “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band, “IEEE Trans. Microwave Theory and Techniques, 47(11), 2059-2074, (1999), hereby incorporated by reference), and magnetic conductors (see, O. Luukkonen, C. R. Simovski, and S. A. Tretyakov. Grounded uniaxial material slabs as magnetic conductors, Progress In Electromagnetics Research B, 15, 267-283 (2009), hereby incorporated by reference.
At THz frequencies, active electromagnetic composites have been developed including voltage controlled modulators and phase shifters, and reconfigurable materials as reported in H. T. Chen, et al., Active terahertz metamaterial devices, Nature, 444, 597 (2006), H. T. Chen, et al., Experimental demonstration of frequency-agile terahertz metamaterials, Nature Photonics, 2, 295 (2008), and H. Tao, et al., Reconfigurable Terahertz Metamaterials, Phys. Rev. Lett., 103, 147401 (2009). All of these devices were created through precise design of metallo-dielectric unit cells. The geometry of the metallic structure within the unit cell imbues the composite with macroscopic properties not found in its constituent components. As with atomic materials, the point group symmetry of the unit cell maps onto the macroscopic properties. A prime example are unit cells the lack fourfold rotational symmetry which manifests as birefringence in the material response. This lack of symmetry has been previously exploited to make transmissive waveplates as referenced in A. C. Strikwerda, Fan, Hu Tao, D. V. Pilon, X. Zhang, and R. D. Averitt, Comparison of birefringent electric split-ring resonator and meanderline structures as quarter-wave plates at terahertz frequencies, Opt. Express 17, 136-149 (2009), X. G. Peralta, E. I. Smirnova, A. K. Azad, H.-T. Chen, A. J. Taylor, I. Brener, and J. F. O'Hara, Metamaterials for THz polarimetric devices, Opt. Express 17, 773-783 (2009), and P. Weis, O. Paul, C. Imhof, R. Beigang, and M. Rahm, “Strongly birefringent metamaterials as negative index terahertz wave plates,” Appl. Phys. Lett. 95, 171104 (2009). However these, and other typical THz components, suffer high insertion loss which arises from Fresnel losses which can be substantial as typical materials at THz frequencies have large refractive indices. This can be remedied through the use of anti-reflection (AR) coatings, but in foregoing references (A. C. Strikwerda, Fan, Hu Tao, D. V. Pilon, X. Zhang, and R. D. Averitt, “Comparison of birefringent electric split-ring resonator and meanderline structures as quarter-wave plates at terahertz frequencies,” Opt. Express 17, 136-149 (2009), X. G. Peralta, E. I. Smirnova, A. K. Azad, H.-T. Chen, A. J. Taylor, I. Brener, and J. F. O'Hara, Metamaterials for THz polarimetric devices, Opt. Express 17, 773-783 (2009), and P. Weis, O. Paul, C. Imhof, R. Beigang, and M. Rahm, “Strongly birefringent metamaterials as negative index terahertz wave plates,” Appl. Phys. Lett. 95, 171104 (2009)) the AR coatings would be thicker than the actual device, which may be disadvantageous in either fabrication or implementation.
In P. Weiss, et al., “Strongly birefringent metamaterials as negative index terahertz wave plates,” Applied Physics Letters 95, 171104 (2009) (hereby incorporated by reference), there is reported an alternative approach for the design and fabrication of thin wave plates with high transmission in the terahertz regime. The wave plates are based on strongly birefringent cut-wire-pair metamaterials that exhibit refractive indices of opposite signs for orthogonal polarization components of an incident wave.
Referring now to FIG. 1, a half waveplate rotates linearly polarized light by 90 degrees. A quarter waveplate converts linearly polarized light into circularly polarized light.